1. Field of the Invention.
This invention relates to a polishing pad used for the grinding, lapping, shaping and polishing of semiconductor substrates, wafers, metallurgical samples, memory disk surfaces, optical component, lenses, wafer masks and the like. More particularly, the present invention relates to polishing pads used in the chemical mechanical polishing of a semiconductor substrate and methods for their use.
2. Discussion of the Related Art.
A semiconductor wafer typically includes a substrate, such as a silicon or gallium arsenide wafer, on which a plurality of integrated circuits have been formed. Integrated circuits are chemically and physically integrated into a substrate by patterning regions in the substrate and layers on the substrate. The layers are generally formed of materials having either a conductive, insulating or semiconducting nature. In order for a device to have high yields, it is crucial to start with a flat semiconductor wafer and, as a result, it is often necessary to polish a semiconductor wafer. If the process steps of device fabrication are performed on a wafer surface that is not planar, various problems can occur which may result in a large number of inoperable devices. For example, in fabricating modern semiconductor integrated circuits, it is necessary to form conductive lines or similar structures above a previously formed structure. However, prior surface formation often leaves the top surface topography of a wafer highly irregular, with bumps, areas of unequal elevation, troughs, trenches and other similar types of surface irregularities. Global planarization of such surfaces is necessary to ensure adequate depth of focus during photolithography, as well as removing any irregularities and surface imperfections during the sequential stages of the fabrication process.
Although several techniques exist to ensure wafer surface planarity, processes employing chemical mechanical planarization or polishing techniques have achieved widespread usage to planarize the surface of wafers during the various stages of device fabrication in order to improve yield, performance and reliability. In general, chemical mechanical polishing ("CMP") involves the circular motion of a wafer under a controlled downward pressure with a polishing pad saturated with a conventional, typically chemically-active, polishing slurry.
Typical polishing pads available for polishing applications, such as CMP, are manufactured using both soft and rigid pad materials and may be classified in three groups: polymer-impregnated fabrics; microporous films and cellular polymer foams. For example, a pad containing a polyurethane resin impregnated into a polyester non-woven fabric is illustrative of the first group. Such pads, illustrated in FIGS. 1 and 2, are commonly manufactured by preparing a continuous roll or web of fabric; impregnating the fabric with the polymer, generally polyurethane; curing the polymer; and cutting, slicing and buffing the pad to the desired thickness and lateral dimensions.
Polishing pads of the second group, are shown in FIGS. 3 and 4 and consist of microporous urethane films coated onto a base material which is often an impregnated fabric of the first group. These porous films are composed of a series of vertically oriented closed end cylindrical pores.
Polishing pads of the third group are closed cell polymer foams having a bulk porosity which is randomly and uniformly distributed in all three dimensions. An example of such a pad is represented in FIGS. 5 and 6. The volume porosity of closed cells polymer foams is typically discontinuous, thereby inhibiting bulk slurry transport. Where slurry transport is desired, the pads are artificially textured with channels, grooves or perforations to improve lateral slurry transport during polishing. For a more detailed discussion of the three main groups of polishing pads, their benefits and disadvantages, see International Publication No. W096/15887, the specification of which is incorporated herein by reference. Other representative examples of polishing pads are described in U.S. Pat. Nos. 4,728,552, 4,841,680, 4,927,432, 4,954,141, 5,020,283, 5,197,999, 5,212,910, 5,297,364, 5,394,655 and 5,489,233, the specifications of which are also each incorporated herein in their entirety by reference.
In order for CMP and other polishing techniques to provide effective planarization, slurry delivery and distribution to the polishing surface becomes important. For many polishing processes, especially those operating at high rotational speeds or pressures, inadequate slurry flow across the polishing pad may give rise to non-uniform polishing rates, poor surface quality across the substrate or article, or deterioration of the polishing pad. As a result, various efforts have been made to improve slurry delivery. For example, U.S. Pat. No. 5,489,233 to Cook et al. discloses the use of large and small flow channels to permit transport of slurry across the surface of a solid polishing pad. U.S. Pat. No. 5,533,923 to Shamouillian et al. discloses a polishing pad constructed to include conduits which pass through at least a portion of the polishing pad to permit flow of the polishing slurry. Similarly, U.S. Pat. No. 5,554,064 to Breivogel et al. describes a polishing pad containing spaced apart holes to distribute slurry across the pad surface. Alternatively, U.S. Pat. No. 5,562,530 to Runnels et al. disclosed a pulsed-forced system that allows for the down force holding a wafer onto a pad to cycle periodically between minimum (i.e. slurry flows into space between the wafer and pad) and maximum values (slurry squeezed out allowing for the abrasive nature of the pad to erode the wafer surface). U.S. Pat. Nos. 5,489,233, 5,533,923, 5,554,064 and 5,562,530 are each incorporated herein by reference.
Although known polishing pads are suitable for their intended purpose, a need remains for an improved polishing pad which provides effective planarization across an IC substrate, especially for use in CMP processes. In addition, there is a need for polishing pads having improved polishing efficiency, (i.e. increased removal rates), improved slurry delivery (i.e. high and uniform degree of permeability of slurry throughout pad in all directions), improved resistance to corrosive etchants, and localized uniformity across the substrate. There is also a need for polishing pads that can be conditioned by multiple pad conditioning methods and that can be reconditioned many times before having to be replaced.